Central Cutout Research Articles

Localized phase contrast imaging at the Wendelstein 7-X stellarator

In its basic form, phase contrast imaging (PCI) provides line-integrated measurements of electron density fluctuations in plasmas. As turbulent fluctuations in magnetically confined plasmas have wave vectors almost perpendicular to the background magnetic field, the signals scattered by fluctuations from different parts of the PCI line-of-sight (LoS) are spatially separated in focal planes of the plasma. This allows localized PCI measurements by placing a mask in such a plane, to only permit signals from specific parts of the LoS to reach the PCI detectors. The present paper describes modeling and design of localization masks for the PCI system at the Wendelstein 7-X (W7-X) stellarator as well as the first results obtained using the masks in the recent long-pulse W7-X experimental campaign. During this project, we have extended the theory describing the mask response within the Fraunhofer diffraction model. As a novel development, we show from first principles that the mask response is determined by the fraction of power of the scattered beam spots that passes the mask. These insights have been used to select the W7-X mask design, consisting of a circular cutout, allowing the unscattered beam spot to pass the mask, with wedges covering a fixed angular range outside the central cutout. In the recent W7-X experimental campaign, the masks have verified the location of the main turbulence features observed by the PCI system and provided new information about the location of short-wavelength magnetohydrodynamic modes.

Determination and analysis of stress concentration factor in finite plate with different polygonal discontinuities under uniaxial compression using finite element analysis (FEA)

Stress concentration is the accumulation of stress in a body due to a sudden change in its geometry. Stresses and stress concentrations are created at the nearer area of the structural discontinuities. Any structural discontinuity compromises the strength of the structure. Numerical approaches can be used to determine the maximum stress concentration for various complex geometries without regard to time or cost constraints. The current study gives a thorough finite element analysis of stress concentration in a structural steel plate with a polygonal cutout. In contrast to orientation and area, this study looks at an isotropic finite plate for the stress concentration factor (SCF) with central polygonal cutouts (triangular, square, pentagonal, and hexagonal). ANSYS, a finite element program, calculates the von Mises stresses, and based on the results, stress concentrations are calculated. The orientation of polygonal cutouts in a square plate and the constant area of polygonal cutouts in a square plate are two parameters considered in the calculation. These results are verified by literature for the orientation of the hole, which concludes that a square hole position parallels the loading direction showing a 50% reduction in stress concentration factor.

Stability and Failure of Thin-Walled Composite Plate Elements with Asymmetric Configurations.

In the present study, the stability and failure phenomena of thin-walled constructions subjected to axial compression, featuring a central cut-out, and constructed from composite materials were explored. These constructions were fabricated from a carbon-epoxy composite using the autoclave method. The research encompassed experimental assessments on actual specimens alongside numerical analyses employing the finite element approach within the ABAQUS® software. The investigation spanned the entire load spectrum up to the point of structural failure, incorporating both practical trials and simulation analysis. During the practical assessments, the study monitored the post-buckling response and captured acoustic emissions to thoroughly evaluate the composite's failure mechanisms. Additionally, the ARAMIS system's non-invasive three-dimensional scanning was employed to assess deformations. Theoretical simulations utilized a step-by-step failure analysis, initiating with failure onset as per Hashin's theory and proceeding to failure progression based on an energy criterion. The simulation outcomes, particularly concerning the critical and post-critical phases, were juxtaposed with empirical data to identify the composite's vulnerability zones. The comparison underscored a significant concordance between the simulation predictions and the empirical findings.

Comparative Study of Linear Static Analysis of G+10 Storey Building with and Without Shear Wall in ETABS

Planning, designing, and execution of high-raise building while taking into account the impact of lateral loads such as wind and seismic loads computation with or without shear wall technology in conventional mode is a crucial task for civil engineers. The lateral loads develop high lateral stresses and sway movement in structural members and need adequate stiffness to resist lateral forces along with sufficient strength against vertical gravity loads. In this case, civil engineers establish an effective system for construction of high raise building with the usage of shear wall system is high in-plane stiffness and torsional resistance. Present the authors are considered a G+10 storey commercial shopping mall with a central cut-out at Bhimavaram location which lies in seismic zone III as, per IS 1893(part 1): 2016. The load cases from IS 875 Part I (dead loads), Part II (imposed loads), and Part III (wind loads) are used to create the load combinations in accordance with IS 456: 2000. Two models, with and without shear wall system are taken for comparing the parameters like storey drift, storey displacement, stiffness, shear force, base shear, bending moment and center of rigidity by performing linear static seismic analysis and wind analysis for both models in ETABS software. The simulations concluded that Shear wall system is the efficient and economical way of resisting lateral loads in high rise or multistory buildings.

SiO nanoparticle modified CFRP composites effecting on mechanical and vibration damping properties

AbstractSiO nanoparticle inclusion effects on vibration‐damping and mechanical properties of carbon fiber reinforced plastic composites (CFRP) were experimentally investigated by incorporating the NS particles into the epoxy resin system. The nanoparticles in the SiO form were incorporated into the epoxy resin at different ratios (0.5%, 1%, 1.5%, 2%, and 3%) in weight to produce the modified CFRP samples. In addition, the effects of cutout with two different types (edgewise semicircular and central circular) on the vibration response of SiO modified CFRP test samples were determined for different SiO particle incorporation ratios. In this way, variation of both mechanical and vibration properties was experimentally determined in terms of cutout weakening of the composite in the middle while incorporating the SiO particle modification of the CFRP composites. It was seen from this study that the incorporation SiO nanoparticles into CFRP composites were provided the increasing trend in the vibration‐damping and mechanical properties and the highest mechanical and vibration properties were obtained for the addition of 1.5 wt% SiO nanoparticles. On the other hand, further SiO nanoparticle addition, more than 1.5–2 wt%, decreased in mechanical and vibration properties of the composite test samples.Highlights SiO nanoparticle effects on mechanical properties of CFRP composite laminates. SiO nanoparticle effects on vibration damping of CFRP composite laminates. Central cutout effects on vibration characteristics of CFRP composite laminates. Fracture characteristics of CFRP composite laminates with SiO nanoparticle incorporation.

Buckling Analysis of Laminated Plates with Asymmetric Layup by Approximation Method.

This study investigated thin-walled plate elements with a central cut-out under axial compression. The plates were manufactured from epoxy/carbon laminate (CFRP) with an asymmetric layup. The study involved analyzing the buckling and post-buckling behavior of the plates using experimental and numerical methods. The experiments provided the post-buckling equilibrium paths (P-u), which were then used to determine the critical load using the straight-line intersection method. Along with the experiments, a numerical analysis was conducted using the Finite Element Method (FEM) and using the ABAQUS® software. A linear analysis of an eigenvalue problem was conducted, the results of which led to the determination of the critical loads for the developed numerical model. The second part of the calculations involved conducting a non-linear analysis of a plate with an initial geometric imperfection corresponding to structural buckling. The numerical results were validated by the experimental findings, which showed that the numerical model of the structure was correct.

Dynamic analysis of laminated shell panels with cutout and cracked corners carrying concentrated and distributed mass

This article employs Mindlin’s first-order shear deformation theory to analyze the dynamic behavior of laminated composite shells with various geometries, featuring central cutouts and cracked corners that carry concentrated and distributed mass. The formulation considers an isoparametric element with nine nodes and five degrees of freedom per node. Both in-plane and transverse effects of mass are addressed by incorporating lumped mass with rotational inertia in the formulation. The obtained results are compared to previously published data, showing an excellent agreement with a variation of less than ±2.5% for all cases. Following validation, the study examines shell vibration for various geometries carrying concentrated mass, distributed mass, and distributed patch mass. Additionally, the dynamic analysis of shell panels with central cutouts and cracked corners with different cracked dimensions is conducted. Unique boundary conditions are introduced by applying them to both the outer and cutout edges (i.e., SSSS-CCCC, FFFF-CCCC).

Enhancing delamination resistance with intralaminar stiffness tailoring: A numerical study of variable stiffness composites

In general, strategies and techniques involving intralaminar stiffness tailoring are primarily used to improve compressive capacity (buckling and post-buckling) or tensile properties rather than interlaminate toughness for composites. However, in this work, we show the potential of utilizing intralaminar stiffness tailoring to enhance delamination resistance by specifically investigating the perforated variable stiffness composite plate with a different layout of curvilinear fibers. Firstly, a standard finite element model with the typical cohesive interface to evaluate the delamination performance of different composites is established and is verified against the averrable experimental data of intact constant stiffness composites. Then, two kinds of curvilinear fibers for the perforated composite plates under the Mode I and Mode II delamination test are investigated considering the different fiber layouts and the size of the central cutout. The reaction force–displacement curve and the R-curve of the composites with the curvilinear fibers are obtained to show the enhancement effect of the intralaminar stiffness tailoring on the delamination resistance. The interlaminate toughness of the curvilinear fibers laminate can overperform the straight fibers laminate up to 71% and 63% in the mode Ⅰ and mode Ⅱ cases (r = 8). The underlying mechanism is discussed in detail to inspire new ideas for intra-laminar stiffness tailoring to improve interlaminar toughness.

Revisiting the Fibonacci spiral pattern for stiffening rib design

For a long period, phyllotaxis (the arrangement of leaves on a plant stem) has been observed as an interesting morphological property of various plants, and the phyllotactic spirals form a distinctive class of patterns in nature. These days, the unique patterns governed by the Fibonacci sequence, or the golden ratio in a deeper sense, have moved beyond the botanical system and came to be universal, occurring in architectural and structural design. In this work, we develop a design approach for curvilinear stiffening ribs which follow the Fibonacci spiral pattern. The parametric model of the designed ribs is built according to two parameters, one discrete and another continuous. Parametric studies on the two variables are performed to assess the potential mechanical advantages of the Fibonacci spiral pattern in stiffening structures. The deformation-, vibration- and buckling-resisting capacities are investigated for thin-walled stiffening plates with a central cutout. Moreover, an attempt is devoted to clarifying the rationality of curvilinear stiffening ribs’ employment in other designs. Lastly, we demonstrate that the developed protocol does not limit itself to planar structures with cutouts, and it is easy to be extended to stiffening ribs on curved surfaces, where the gain in mechanical property is observed to be even more visible and pronounced.

Effect of angle-ply arrangement on fracture behaviour of FRP composite laminate under the thermal loading conditions subjected to central elliptical cut-out

ABSTRACT The crack propagation in composite material due to thermal loading and environmental conditions is a serious issue. The study of the fracture propagation in a composite laminate will help understand the response of the structures under various loads. In the present study, a composite laminate is modelled with an elliptical cut-out and the fracture behaviour of the structure under the application of the thermal load is studied. Finite element analysis was used to obtain the stresses in the structure. Thermal load is applied on the laminate in the form of a constant temperature. The temperatures used in the present study are 30°C, 80°C, 130°C, and 180°C. The stresses in the laminate increased with the increase in the thermal load. The stresses in the normal direction are major stresses in the structure. The stresses in the composite laminate at the thermal load of 180°C is nearly nine times the stress at the 30°C in certain conditions.

Using Laurent’s series in the theoretical solution to estimate the stress resultants of FG-CNTRC plates weakened by a central cutout at different temperatures

Conventional ordinary materials have many weaknesses when exposed to extreme loadings. Hence, scientists develop novel engineered materials to address these weaknesses. Functionally Graded Carbon Nanotube Reinforced Composites (FG-CNTRCs) are a modern group of materials that have recently flourished thanks to their excellent and unique mechanical properties. One common loading condition is subjecting FG-CNTRC plates containing cutouts to in-plane loadings. The presence of an opening disturbs the stress field, especially in the proximity of the cutout, and creates stress concentration. This study estimates the stress and moment resultants on the edge of elliptical cutouts in asymmetric FG-CNTRC plates under various loading conditions using a new analysis based on Lekhnitskii’s complex variables method, mapping function, and Laurent series. Unlike previous studies on perforated asymmetric plates, which were based on numerical methods or the Schwartz formulations, this study presents a new solution using Laurent’s series to represent the holomorphic function. In calculating the stress and moment components around the opening, the effect of determining variables is studied. This approach can be generalized to solve different anisotropic body problems (FG_CNTRC, FGM, Laminate composites). Thus, stress and moment components in perforated anisotropic plates can be determined simply and systematically using this method.

Design and analysis of angle-ply arrangement on fracture properties of FRP composite structure under thermo-mechanical loading conditions subjected to central circle cut-out

Design and analysis of angle-ply arrangement on fracture properties of FRP composite structure under thermo-mechanical loading conditions subjected to central circle cut-out

Linear, nonlinear and post buckling analysis of a stiffened panel with cutouts

Stiffeners are typically used to strengthen structures that rely on plates for load bearing. Such structures are subjected to various kinds of in-plane and out-of-plane loading over its lifespan. Furthermore, cutouts in aerospace structures are considered for practical and design reasons. In the present paper, finite element method is used for the analysis of a flat rectangular stiffened plate. Static analysis is performed on three panels with different stiffener cross sections (I section, hat section and rectangular section), and the panel with the least deformation and stress is chosen for further buckling analysis. Linear, non-linear and post buckling analysis of the selected stiffened panel under in-plane compression is carried out and its load and end – shortening response is evaluated till collapse. Furthermore, the effect of rectangular and circular central cutouts on the buckling behaviour of the stiffened panel is investigated. By varying the dimensions of the cutouts, a parametric study on buckling and ultimate collapse strength is performed. The study takes into account an aluminium alloy with isotropic material properties and a carbon fibre reinforced polymer (CFRP) with orthotropic material properties.

The Impact of the Cut-Out Shape on the Dynamic Behavior of Composite Thin Circular Plates

This study measures the impact of the cut-out shape on the fundamental frequency and the harmonic response of thin composite circular plates under fixed boundary conditions. For this purpose, the Finite Element Method has been employed using the SHELL181 element of ANSYS Workbench 18.2 software. Nine different circular plates having central equilateral triangle, square, regular pentagon, regular hexagon, regular heptagon, regular octagon, regular nonagon, regular decagon, and circular cut-outs have been designed to understand the changes in the vibrational behavior of a structure as the cut-out geometry approximates to circular. Additionally, a solid circular plate has been modelled for comparison purposes. To investigate the effect of the cut-out shape more deeply, all structures have been designed as cross-ply and angle-ply composites. The free vibration analysis has been performed to obtain the fundamental frequency of each structure. The harmonic response analysis problem has been solved by employing the Mode Superposition Method and considering a constant damping ratio. The results of the study have been interpreted by considering the displacement response, stress, and phase shifts at a certain frequency range. The results indicate that the shape of the cut-out considerably affects the fundamental frequency and harmonic response of the circular structure regardless of its fiber orientation.

Flexural strength recovery of RC one-way slabs having cut-outs using NSM-SHCC plates

Creating a cut-out in an existing Reinforced Concrete (RC) slab became a common practice to allow passing facility services. This cut-out interrupts the loading trajectories resulting in the existence of weak points. Thus, the ultimate capacity of such slab including cut-out decreases with the increase of the size of the opening. In this paper, a new technique based on near-surface mounted has been employed using precast plates made of Strain-Hardening Cementitious Composites (SHCC). These SHCC plates were designed to compensate the cut reinforcement due to cut-out. The used plates had three different widths; 100, 200 and 300 mm, while their thickness was kept constant at 20 mm. One reference slab without cut-out, in addition to, nine damaged slabs with central cut-outs, were prepared and tested under incremental static loading. The tested slabs have the same dimensions; thickness = 140, effective depth = 120 mm, width = 1200 mm and span = 2200 mm. For the cut-out, a rectangular shape with constant width of 200 mm has been used, while the length parallel to the supporting line was varied considering three values; 200, 400, and 600 mm. All slabs were reinforced with a single bottom steel mesh with a longitudinal reinforcement ratio of 0.65%. The slabs having cut-outs were divided into three groups (I, II and III); each one included three different cut-outs. The slabs of group I were tested without strengthening. On the other hand, group II was strengthened at the tension side only, whereas, group III was strengthened at both tension and compression sides. Based on the experimental findings, the load-carrying capacities of group II raised by 15–57% compared to group I; however, this increase was accompanied by a significant decrease in the developed ductility where the displacement-based ductility index could be dropped by 58% for the slab having cut-out length of 600 mm. For group III, the application of SHCC plates at both tension and compression sides enabled the strengthened slabs to restore nearly the lost capacity resulting from providing the cut-out with a good ductility performance.

Buckling Analysis and Optimization of Stiffened Variable Angle Tow Laminates with a Cutout Considering Manufacturing Constraints

Variable angle tow laminates (VAT) and stiffeners are known to redistribute the in-plane load distribution and tailor the buckling mode shapes, respectively, for improving structural performance. To leverage the benefits of using VAT laminates in the practical applications, in the present paper, we discuss buckling load maximization conducted for a stiffened VAT laminated plate with a central cutout considering VAT laminate manufacturing constraints. Three representative boundary conditions as seen in the aerospace structures are considered: in-plane axial displacement, in-plane pure shear, and in-plane pure bending displacements. Two common manufacturing constraints, the one on the automatic fiber placement (AFP) manufacturing head turning radius and the other on the tow gap/overlap, while fabricating VAT laminates are considered in the laminate design. These two manufacturing constraints are modeled by controlling the fiber path radius of curvature and tape parallelism in optimizing the fiber path orientations for the VAT laminates. Stiffener layout and fiber path angle for the VAT laminated plates are both considered in the buckling load maximization study. To avoid using a fine mesh in modeling the stiffened VAT laminates with a cutout when employing the finite element analysis during the optimization, the VAT laminated plate and the stiffeners are modeled independently. The displacement compatibility is enforced at the stiffener–plate interfaces to ensure that the stiffeners move with the plate. Particle swarm optimization is used as the optimization algorithm for the buckling load maximization study. Optimization results show that, without considering AFP manufacturing constraints, the VAT laminates can increase the buckling loads by 21.2% and 12.4%, respectively, comparing to the commonly used quasi-isotropic laminates and traditionally straight fiber path laminates for the structure under the in-plane axial displacement case, 19.7% and 12.5%, respectively, for the in-plane shear displacement case, and 62.1% and 26.6%, respectively, for the in-plane bending displacement case. The AFP manufacturing constraints are found to have different impacts on the buckling responses for the VAT laminates, which cause the maximum buckling load to be 9.3–10.1%, 3.0–3.2%, and 23.2–29.8% less than those obtained without considering AFP manufacturing constraints, respectively, for the present studied model under in-plane axial, shear, and bending displacements.

NURBS isogeometric-based nonlinear flexural analysis of quasi-3D surface elastic porous nanoplates

In this research work, by taking the geometrical nonlinearity together with the surface elastic-based types of size dependency, the nonlinear flexural characteristics of quasi-3D porous nanoplates in the presence and absence of a central cutout are examined via an efficient numerical strategy. Regarding to this issue, the non-uniform rational B-spline (NURBS) are put to the isogeometric methodology in order to satisfy the necessary requirements associated with the C−1-continuity. The constructed surface elastic-based plate model contains sinusoidal distribution for the shear and normal deflections by incorporating only four variables to reduce the computational cost significantly. The porosity dependency is taken into account based upon various patterns of porosity dispersion through the nanoplate thickness. The surface elastic-based nonlinear flexural responses are achieved for complete and incomplete nanoplates having central cutouts with different edge supports. It is revealed that the gap between nonlinear bending curves associated with various patterns of porosity dispersion is a bit higher for a nanoplate with lower plate thickness in which the role of surface elasticity is more significant due to a higher surface to volume ratio.

Nonlinear Large-Amplitude Oscillations of PFG Composite Rectangular Microplates Based Upon the Modified Strain Gradient Elasticity Theory

In this research work, the nonlinear large-amplitude free vibration characteristics of composite microplates made of a porous functionally graded (PFG) material are addressed numerically in the presence of different size-dependent strain gradient tensors as microscale. Accordingly, for the first time, the effect of each microstructural tensor is analyzed separately on the nonlinear free oscillations of PFG microplates with and without a central cutout. In order to fulfill this goal, the isogeometric computation approach is engaged to integrate the finite element approach into the nonuniform B-spline-based computer aided design tool. Accordingly, the geometry of the microplate with a central cutout is modeled smoothly to verify C−1 continuity based upon a refined higher-order plate formulations. In this regard, the microstructural-dependent frequency responses associated with the nonlinear free oscillations of microplates are traced. In both the cases of simply supported and clamped boundary conditions, it was revealed that the fundamental frequency is enhanced about 1.20% by considering only the symmetric rotation gradient tensor, about 3.27% by taking only the dilatation gradient tensor, and 9.43% by considering only the deviatoric stretch gradient tensor. On the other hand, the anisotropic character of PFG composite microplates results in an unsymmetrical frequency response curve, as the nonlinear frequencies associated with negative oscillation amplitudes are a bit higher than those of positive ones.

Free vibration analysis of perforated composite cylindrical shell and panel using multi-domain generalized differential quadrature (GDQ) method

Free vibration behavior of a composite shell/panel with and without a central square cutout has been studied using Multi-domain Generalized Differential Quadrature (GDQ) method. A physical domain is decomposed into several elements in such a way that all the elements have uniform thickness and material properties, as well as continuous loading and boundary conditions at their edges. The governing equations are derived based on the first-order shear deformation theory. They are formulated in a general form and can be converted to Donnell’s, Love’s, and Sanders’ theories. In addition, compatibility conditions are considered at the interface boundaries of adjacent elements as well as proper boundary conditions on other elements edges. The GDQ method is employed to discretize these equations in both longitudinal and circumferential directions. By assembling these discretized relations, a system of algebraic equations will be generated. These equations can be solved throughan eigenvalue solution to compute the natural frequencies of the whole shell/panel. Numerical results obtained by the presented method are compared with ABAQUS results and those available in the literature. After verifying the accuracy and precision of the proposed method, it is employed to study the effect of an opening on the vibrational behavior of composite shells and panels through a parametric study. The influence of the presence of a cutout and its size is investigated on shells/panels with various material properties, layup orientations, thicknesses, dimensions, and boundary conditions. The obtained results can be used as a benchmark for further researches.

Nonlinear Stability Characteristics of Porous Graded Composite Microplates Including Various Microstructural-Dependent Strain Gradient Tensors

In this study, the nonlinear buckling and postbuckling characteristics of composite microplates made of a porous functionally graded (PFG) material are scrutinized in the presence of different size-dependent strain gradient tensors as microscale. Accordingly, for the first time, the effect of each microstructural tensor is analyzed separately on the nonlinear stability of PFG microplates with and without a central cutout. In order to fulfill this goal, the isogeometric computation approach is engaged to integrate the finite element approach into the nonuniform B-spline-based computer aided design tool. Accordingly, the geometry of the microplate with a central cutout is modeled smoothly to verify [Formula: see text] continuity based upon a refined higher-order plate formulations. In this regard, the microstructural-dependent load-deflection paths associated with the nonlinear stability of axially compressed microplates are traced.